Contact lenses comprise a central zone called optical zone and a peripheral zone for the fastening of the lens. The contact lenses are always in movement on the eye, these movements being linear or rotative.
The spherical optical corrections are not affected by movements, all other types of correction however, of the astigmatic, prismatic, bi- and multifocal type are oriented optical corrections for which any rotation must be avoided.
Known means for stabilizing these rotations are of two types, however similar in that they are based on the prismatic shape of the lense. In the first type the means is a monoprismatic shape with the greatest thickness at the lower border. The weight of this border, thus increased, makes rocking the lens into the desired position by successive oscillations. Sometimes the lower border is truncated for increasing stability. In the second type the means is a bi-prismatic shape with the greatest thickness horizontal at the center of the lens. The stabilization is obtained by the pressure of the eyelids on two inclined planes.
The German Publication No. 2 046 389 discloses a contact lens with one reinforcement at the lower part of the extreme border, which hinders the sinking down of the lens and enables the centering of the contact lens. This one reinforcement does not completely avoid rotation of the lens and the lens becomes relatively thick.
The published European Patent Application No. 0 008 726 discloses a contact lens having a toric and a prismatic part as mentioned above, the prismatic part increasing the thickness of the lens.